The technical scope of the invention is that of projectiles incorporating a sub-calibre penetrator positioned in a full calibre sabot.
The sabot is made of a light material, for example aluminum, and is classically formed of several segments (more often than not, three) which surround the penetrator. The segments are linked together by a band that ensure gas tightness within the gun barrel and one or two retention rings, located to the fore or rear of the sabot, or on a front guiding seat.
The sabot enables the penetrator to be fired from the gun barrel. It releases the penetrator upon exiting the barrel.
The penetrator and the sabot generally incorporate profiles cooperating with each other so as to ensure the axial drive of the penetrator by the sabot when the projectile is being fired. These profiles may comprise helicoidal threading on the penetrator housed in female threading in the sabot or else a succession of teeth and ring-shaped grooves.
Patent FR2666647 describes such a known projectile.
Classical drive profiles are designed so as to supply the sabot with a bearing surface enabling it to transmit the longitudinal thrusting stresses, created by the action of the powder gases, to the penetrator. This profile is thus essentially dimensioned to withstand shearing.
Classical profiles are either so-called ISO profiles (in which the teeth are trapezoidal and symmetrical with respect to the transversal plane) or artillery profiles (in which the teeth are not symmetrical but have a rear flank strongly inclined with respect to the penetrator's axis).
When a projectile incorporating a drive profile of a known type moves through the barrel of a weapon, it is subjected to a certain number of transversal disturbances caused by the curvature of the barrel, pressure dissymmetry and the projectile's own vibrations which cause flexions in the penetrator.
The three sabot segments thus work independently of each other and at any given moment there are only one or two segments supporting the penetrator in flexion. The sabot, therefore, does not help the penetrator to withstand flexion.
These segment movements are all the greater in that the penetrator is long (L/D elongation over 25).
Moreover, through the combined action of its inertia, the pressure stresses and traversal accelerations, the sabot can start to open at its front pocket. In this case, the support it gives to the penetrator is reduced.
Deficiencies in the support of the penetrator lead to firing obliquities and a loss of accuracy.
Furthermore, when the front of the sabot opens like this, the guiding seats create greater friction with the barrel, thus aggravating its wear.